Coiled tubing is often used for drilling and servicing oil and gas wells. Coiled tubing is flexible, small-diameter continuous steel tubing. In drilling operations, coiled tubing may be used for drilling wells that deviate from vertical. The coiled tubing conveys drilling fluid to a downhole drilling motor that drives a drill bit for drilling. In servicing operations, coiled tubing may be used for logging, cleaning, initiating flow, well simulation, and cementing. Coiled tubing generally reduces trip time compared to jointed tubing.
Several types of emergency releases have been used for disconnecting a stuck downhole tool from coiled tubing. For example, shear disconnects, hydraulic disconnects and electrical disconnects have been used. Such disconnects typically include upper and lower sections with seals to prevent leakage.
Shear connects use shear pins or screws that hold the sections together. In the event the downhole tool becomes stuck in the well, the coiled tubing is pulled with sufficient tension to break the cumulative shear pin's strength. Hydraulic disconnects are typically ball-activated release devices. Hydraulic disconnects are capable of holding high tension and pressure because they are pressure-balanced. Electrical disconnects release the downhole tool from the coiled tubing by applying an electrical signal through a wire to the release device.